Hot or cold rolling of strip or plate

ABSTRACT

THIS INVENTION RELATES TO THE HOT OR COLD ROLLING OF STRIP OR PLATE TO A SUBSTANTIALLY CONSTANT PROFILE, AND PROVIDES A METHOD OF ROLLING IN WHICH THE TOTAL ROLLING FORCE IS SENSED DURING ROLLING OF THE MATERIAL, AND IN WHICH THE MAGNITUDES OF ROLL-BENDING FORCES AND MOMENTS APPLIED TO THE ROLLS ARE INDEPENDENTLY AND SIMULTANEOUSLY VARIED IN PROPORTION TO CHANGES IN THE TOTAL ROLLING FORCE SO AS TO MAINTAIN SUBSTANTIALLY CONSTANT THE DESIRED PROFILE OF THE ROLLED MATERIAL.

B. SABATlNl ET AL HOT OR COLD ROLLING OF STRIP OR PLATE Nov. 16, 1971 2. Sheets-Sheet 1 Filed July 7, 1969 NOV. 16, 197] B'SABJQAT1N1 ET AL 3,620,058

HOT OR com) ROLLING OFF-STRIP OR PLATE Filed July 7, 1969 2 Sheets-Sheet 2 lL////l Fla. 2.

United States Patent 3,620,058 HOT OR COLD ROLLING OF STRIP 0R PLATE Bruno Sabatini, Thames Ditton, Surrey, and Kenneth A. Yeomans, Worksop, England, assignors to The British Iron and Steel Research Association Filed July 7, 1969, Ser. No. 839,506 Claims priority, application Great Britain, July 9, 1968, 32,756/ 68 Int. Cl. B211) 37/12 US. Cl. 72-8 3 Claims ABSTRACT OF THE DISCLOSURE This invention relates to the hot or cold rolling of strip or plate to a substantially constant profile, and provides a method of rolling in which the total rolling force is sensed during rolling of the material, and in which the magnitudes of roll-bending forces and moments applied to the rolls are independently and simultaneously varied in proportion to changes in the total rolling force so as to maintain substantially constant the desired profile of the rolled material.

The present invention relates to the hot or cold rolling of strip or plate and offers a solution to the problem of controlling the transverse thickness profile of the rolled product in the face of rolling load variations occurring during the rolling operation.

The transverse thickness profile (later simply referred to as profile) imparted to strip or plate in hot rolling is important because of the general requirement for dimensional accuracy and consistency of the product and also in relation to subsequent cold rolling of hot rolled strip.

Profile changes are frequent in present day hot rolling practice due to rolling force variations brought about by deviations in stockpiece temperature and chemical composition. The consequences of such deviations in terms of profile changes can be further exacerbated by automatic thickness control systems using screw-down action.

It is an aim of the invention to provide apparatus and a method of rolling which ensures constant strip profiles from the hot mill irrespective of any rolling load variations however originated during the rolling operation. Such apparatus and method would greatly simplify the shape control problem in the cold stage of strip rolling by eliminating input profile changes to cold mill. The apparatus and method would also be applicable to plate rolling and rolling of strip not to be subsequently cold rolled.

According to the invention there is provided apparatus for rolling strip material, comprising first means for sensing the total rolling force during rolling of the material, second means for applying a roll-bending force to the rolls, third means for applying roll-bending moments to the rolls, and control means operable to independently and simultaneously vary the force and moment magnitudes applied by the second and third means respectively, in proportion to changes in the total rolling force so as to maintain substantially constant the desired profile of the rolled strip material.

According to the invention there is also provided a method of rolling strip material comprising the steps of sensing the total rolling force during rolling of the material, applying roll-bending forces and moments to the rolls, and independently and simultaneously varying the magnitudes of the forces and moments in proportion to changes in the total rolling force so as to maintain substantially constant the desired profile of the rolled strip material.

We have found that in flat hot rolling the profile emerging from a stand is substantially determined by the stand dimensions, screw setting and roll contour and by the total rolling force developed in the roll gap and any forces or bending moments externally applied to deflect the rolls, but it is substantially independent of the actual profile of the input material.

We have found that by correct set up of the rolling stand or suitable adjustment of it by, for example, differential screwdown, the rolled profiles are symmetrical about the mid-width and any thickness deviations across the strip or plate width from centre line values can be adequately expressed as follows:

h(x) =thickness at distance x from centre line, x=distance from strip or plate centre line,

Iz =thickness at centre line,

P=constant, referred to as parabolic profile parameter, Q=constant, referred to as quartic profile parameter.

We have found that, around any initial operating condition, profile parameter changes and changes in the forces acting on the rolling stand are linearly related, that is:

where From (2) a method can be derived for maintaining the profile parameters P and Q at magnitudes P* and Q* during rolling in spite of changes in rolling force F, provided the externally applied roll-bending force magnitude J and roll-bending moment magnitude M can be simultaneously and independently controlled.

From (2) it is seen that for:

P=P* Q=Q* it is necessaryand sufficient that:

PF' PJ "i-PM' OQF' J' +QM' (4) is a system of two linear equations in the three variables F, J, M and can therefore be solved for any assigned value of one of them. Choosing F as independent variable and solving Equations 4 we have PJ QM PM QJ If I and M are controlled according to (5) and (6) the profile parameters P and Q are held equal to P* and Q* irrespective of rolling force F variations.

The significance of requirement (9) is that the two control means applying magnitudes J and M must be such not to cause profile changes geometrically similar. Thus any roll contour control means applying magnitude M and which satisfies this condition can be used. For example, the means may apply a couple in the vertical plane and/ or a. couple in the horizontal plane, as described in our patent application No. 54,970/ 67.

For the rolling situations of interest the six unit control coefficients a 11 etc. in (7) and (8) are either theoretically calculated or experimentally measured and the values made available for use by the control system when required (see later).

The theoretical calculation of the six unit control coefficients u a etc. can be done using a theoretical model of the rolling stand by simulating small variations in the magnitudes J, M, F and computing the corresponding changes in profile parameters P and Q. The ratio of corresponding changes is the unit control coefficient of interest.

The experimental calculation of the six unit control coefiicients is done by causing changes in magnitudes J, M and F and measuring the corresponding profile parameters changes. Again, the ratio of corresponding changes is the unit "control coefficient. Changes in F can be caused in one or more of the following ways: Small changes in the reduction taken, small changes in the rolling tension, etc. We have found that any one of the above methods gives practically the same result.

An embodiment of the invention will now be described by way of example only in conjunction with the accompanying drawings, in which:

FIG. 1 shows diagrammatically rolling apparatus according to the invention; and

FIG. 2 is a section along the line AA of FIG. 1.

Referring to the drawings, the rolling apparatus R includes a four-high rolling stand including frame, Workrolls 2 and backup rolls 3. The backup rolls 3 are connected to each other at each end by chocks 4 and a pair of force-transmitting links or jacks 5. The rolling load is applied to rolls 2 and 3 through rods 7 of screw-down devices (not shown) positioned at each end of the stand; the total rolling load during rolling is sensed by load cells 8 between the rods 7 and the respective one of chocks 4.

Conveniently, each facing pair of necks of work-rolls 2 is connected together by four chocks 10 and two pairs of force-transmitting links or jacks 11 and 12 spaced axially of the workroll necks; each pair of jacks 11 and 12 is disposed with one jack on each of opposite sides of the workroll neck and together are operable to enable forces to be effectively applied at two spaced points along the neck of respective workroll necks to control the chamber or profile of the workrolls. The jacks are controllable to apply the required bending moment M and/ or the required resultant jack force I to the workrolls; if only a pure bending moment is required then the forces of jacks 11 and 12 must be of equal magnitude and opposite direction.

A profile or detecting instrument 20 such as that described in our copending application No. 14,325/68 is provided downstream of the rolling apparatus R to check the profile of the strip S leaving the rolling apparatus during the initial rolling operation to obtain the desired output profile by suitable adjustments of the available control parameters of the rolling apparatus such as screw setting, rolling tension, roll-bending forces, etc. Signals representing P, Q, F, J and M are fed into a computer C into which are already stored the six unit control coefficients; at the instant when magnitudes P* and Q* are obtained (i.e. desired profile is attained), the computer is put into a HODD condition to store magnitudes of F, J and M at that instant which will then represent F*, J and M The total rolling force F is then continuously measured and corresponding adjustments to J and M values to be applied to jacks 11 and 12 are calculated in the computer C in accordance with Equations 5 and 6, and the necessary correcting signals are fed from the computer to the jacks. To perform the necessary calculations the computer will use the wanted values P*, Q* of the profile parameters (together with the corresponding values F J M of the applied forces) and the values of the unit control coefficients previously referred to.

The bending force and bending moment magnitudes J and M respectively may be applied in a different manner to that described above and for a description of alternative modes of operation, reference is made to our copending application No. 54,970/67; for example, the jacks 11 and 12 may act between the necks of the workrolls and backup rolls.

We claim:

1. Apparatus for rolling strip or plate material, comprising first means for sensing the total rolling force during rolling of the material, second means for applying a roll-bending force to rolling rolls, third means for applying roll-bending moments to the rolls, and control means operable to independently and simultaneously vary the force and moment magnitudes applied by the second and third means respectively, in proportion to changes in the total rolling force so as to maintain substantially constant the desired profile of the rolled material, wherein the control means includes a computer for computing said force and moment values from the two equations:

where J and M:the magnitudes of bending forces and bending moments respectively to be externally applied to the rolls to correct a change in total rolling force,

1* and M= =magnitudes of bending forces and bending moments which are applied to the roll when the mill is initially set to roll the desired profile,

F and F*=the magnitudes of total rolling force sensed during rolling and the total rolling force that occurs when the mill is initially set to roll the desired profile respectively A w: Lori PJ QM PM QJ gal on a PF QJ PJ QM 'RM QJ PF' PJ' PM a 'a 'a =constants 2. A method of rolling strip or plate materials comprising the steps of sensing the total rolling force during rolling of the material, applying roll-bending forces and moments to the rolls, and independently and simultaneously varying the magnitudes of the forces and moments in proportion to changes in the total rolling force so as to maintain substantially constant the desired profile 0f the rolled material, and including the step of computing by means of a computer the magnitudes of the forces and moments from the two equations:

where J and M the magnitudes of bending forces and bending moments respectively to be externally applied to the rolls to correct a change in total rolling force.

1* and M*=magnitudes of bending forces and bending moments which are applied to the roll when the mill is initially set up to roll to desired profile,

F and F*=the magnitudes of total rolling force sensed during rolling and the calculated or measured magnitudes of total rolling force that occurs when the mill is initially set to roll the desired profile,

steps of initially adjusting F, I and M until the desired profile is attained during rolling, then holding in the computer values for F*, 1* and M*, and then continuously sensing the magnitude of F to provide a signal which is fed into the computer to enable the computation of the required adjustments of the magnitudes of J and M.

References Cited UNITED STATES PATENTS 3,213,655 10/1965 Reid 72--11 3,318,124 5/1967 Plaisted 728 3,394,566 7/1968 OBrien 7221 X 3,416,341 12/1968 Dey et a1. 7221 X 3,461,705 8/1969 Neumann 72243 3,475,935 11/1969 Kajiwara 729 3,507,138 4/1970 Neuber 72237 3,531,960 10/1970 Stone 72245 X MILTON S. MEHR, Primary Examiner US. Cl. X.R. 7216, 19 l 

